Ranging system



Nov. 29, 1960 L. BATCHELDER RANGING sYs'rx-:M

2 Sheets-Sheet 1 Filed Feb. 1, 1945 Nov. 29, 1960 BATcHl-:LDER 2,962,694

RANGING SYSTEM Filed Feb. 1, 1945 2 Sheets-Sheet 2 FROM PHASE SENSITIVEDETECTOR Acg FROM PHASE SENSITIVE DETECTOR 57 /58 i' Y; WV

IN VEN TOR. LAURENCE BATCHELDER Hls ATToR EY 2,962,694 Patented Nov. 29,1969 RANGING SYSTEM Laurence Batchelder, Cambridge, Mass., assigner, by

mesne assignments, to Raytheon Company, a corporation of Delaware FiledFeb. 1, 1945, Ser. No. 575,692

13 Claims. (Cl. 340`3) The present invention relates to a ranging systemfor the determination of distance and direction of an object beingsearched and more particularly to such a system operating in a watermedium for the detection of surface vessels and submarines.

The present invention may be used for both commercial and militarypurposes for the prevention of collisions at sea, for guiding a vesselor, when used for military purposes, to detect the presence of a hostilesurface vessel or submarine.

At the present time various systems and `devices have been adopted, sometending towards automatic direction and distance measurement by sweepinga compressional wave beam about an arc and detecting the presence of a`distant object by the receipt of an echo which is picked up by arotatable receiver; the transmitter and receiver operating inestablished sequence so that if a signal or echo is received, thedistance and direction will automatically be established. The presentinvention relates to this type of system but provides certain advantagesover other systems, particularly in the method of indication of the echoand in the elimination of noises and reverberations from the system.

Due to the fact that the transmitter in the present system must transmitover a comparatively long period of time and thereafter the receivermust be sensitive to pick up the echoes, disturbances by way ofreverberations and sounds will be impressed upon the receiver and makeit diicult to pick up and amplify the echoes which of their nature areusually of lower intensity than the local reverberations. In order toovercome this in the present invention a frequency Varying beam ofcompressional waves is swept over the arc which is being observed, thefrequency at the end of the sweep being `considerably different fromthat at the beginning of the sweep so that when the receiving projectoris ready to pick up the echo, the last frequency which was sent isconsiderably different from the echo which is returning.

A further advantage in the present system is the use of a catho-de raytube in which the cathode ray beam is rotated corresponding in angularvelocity to the rotation of the sound beam and in radius to the range ofthe object which is being observed. The system also includes a method bywhich the range may be corrected. This is effected by having thereceiving echoes control the speed of rotation of the transmitting andreceiving projectors. The receiving means establishes whether thereceiving projector is leading or lagging in its rotation the range ofthe echo received and by this means a correction is applied to increaseor `decrease slightly the angular velocity of the rotating projector andreceiver for establishing the correct range.

The present invention has a further advantage in this respect that suchcorrections are made without relying upon an accumulation of successivesignals or echoes which are often confused and intermingled withextraneous reverberations and sound pulses picked up by the receiver.

Other and further advantages of the present Yinvention will be morereadily understood from the description in the rest of the specificationset forth below when taken in connection with the drawings illustratingan embodiment of the invention in which Fig. 1 shows an electricaldiagram of the system with most elements indicated by legends; Fig. 2shows a detail of a portion of the arrangement of Fig. 1; and Fig. 3shows a detail illustrating the means of automatic range correctionmentioned briey above.

In Fig. l, 1 represents the transmitting projector which may transmit asupersonic beam of sound energy by any of the usual well-known meanssuch as magnetostriction, piezoelectric or electrodynamic elements. Sucha projector together with a receiving projector 2 are mounted forrotation on a shaft `3 which is rotated at an angular velocity which isthe same as the angular velocity of rotation of other elements in thesystem as will be explained later. The transmitting and receivingprojector, while shown as mounted on the same shaft, may be rotatedindependently at the same velocities. In the present arrangement firstthe projector sweeps over a given sector of arc and then the receiversweeps over the same sector of arc. As indicated in Fig. 1 for thispurpose the projector and receiver may be arranged back to back with theprojector transmitting for one-half revolution sweeping 180 and thereceiver receiving for the second one-half of the revolution sweepingthe same 180. However if the projector and receiver are rotatedindependently, the projector may transmit every other revolutionsweeping 360, the receiver receiving for the alternate revolutionssweeping 360 while the transmitter is not operating. In the back to backarrangement shown in Fig. l if less than 180 is swept by thetransmitter, there will be an interval between sending and reception.For instance, if the transmitter is swept through a forward arc of therewill be a silent period for 60 before the receiver will act to rangeover the sector through which the beam was transmitted.

The transmitter 1 is supplied by the power amplifier 13 controlledthrough a varying frequency f produced by the variable oscillator 4 thefrequency of which is controlled by means of the reactor tube 5 and apotentiometer 6 over which the rotating arm 8 sweeps at an angularvelocity of 2 w which is twice the angular velocity at which therotating projectors and receivers are rotated. By this arrangement acontinuously upwardly or downwardly varying frequency will betransmitted, the whole sweep of the varying potential arm taking placewhile the transmitting projector is sweeping over the sector beingobserved. For this purpose the potentiometer 6 should be arrangedsubstantially about a 360 circumference. The frequency developed by thevariable oscillator may be established as a value f-l-fo. This frequencyis impressed upon the modulator 9 to which is also impressed a frequencyfo of a xed frequency oscillator 10 which is operated by the keyingcommutator 11 for sending the transmitted signal over the desired arc ofsweep. For this purpose the keying commutator 11 is rotated at anangular velocity tu being the same as the velocity of rotation of thetransmitting and receiving projectors. The modulator 9, which combinesthe frequencies f-l-fo and fo, is connected through a low-pass filter 12to a power amplifier 13 in which only the difference frequency f isamplified because this is the frequency which is passed by the lter 12.The frequency f is delivered to the transmitting projector and convertedinto a supersonic beam of compressional wave at the same frequency or acorresponding frequency. This frequency f will vary continually duringtransmission either from a low to a high frequency or from a high to alow frequency. t

The transmitter 1 may be operated, as mentioned above, for one halfrevolutionpreferably in the forward range of a vessel or for less thanone half revolution. Thereafterit will besilent in accordance with Vthedesign of the keying commutator and willlnotagain 'transmitl until itfaces -in thedesireddirection: In themeantime,`rv

echoV so picked up--will correspond to -a frequencyV in thevaryingrangedependent upon the angular .position at which the echo isreceived. The frequencytpicked up by the receiving projectorswillfbepassed throughthe radio frequency amplifiers 14and15.and-thenthrough the lag lead line 16 to a secondradio frequencyamplifier 17 and-then to the modulator 18 into which it will beimpressed asa frequency f corresponding to the frequency-*atv which-itwas -picked up. There is also impressed upon the modulator 18 thefrequency of the variable oscillatorl 4which iscontinuallychanging-during the receiving cycle in accordance withthe-rotation of the arm-8 toprovide the frequency for reception at themodulator 18- correspondingto that picked up by the receiver 2. ln theoutput of the modulator, therefore, two frequencies are provided, one foand the other 2f+f0. The .high frequency amplifier 19 eliminates thefrequency Z-j-fo and presents to the detector 20 only the frequency fo.This Vfrequency which is beat with the output of the heterodyneoscillator 20 is then irnpressed-upon the audio amplifier 21 to amplifythe beat note obtained and if desired upon.a loud speaker'22.

A rectifier 23 is Yalso connected. to the output of the audio amplifierand this, in turn, is vconnected to the grid 24 of a cathoderay'oscillograph tube 25 forV providing a positive charge forbrighteningvthebeam 26 when the echo-is produced. If the beam issuppressed at other instants, then `the spot made visibleby thebrightening electrode 24 will indicate both the range land vthedirection of the echo andof the observed object or target. The beam ofthe cathode ray tube is deflected from its center by a biasingcurrentapplied to the coils 33 `and 34 and is 'rotated by rotation ofthese coilsat the. angular velocity w mentioned above .by means-of thevmotor 35. The speed of the motor and the current inthe deflection coilare relatedto make the radiusy of the` circlewhich the beam of thecathode ray tube makes a simple func tion of thespeed of they motor andtherefore of theL range of the object being observed. Theback`of-themotor 35 is proportional to its speed and is kfed throughthefilter -39 tothe deflectioncoils 33 and 341v ina polarity toopposeztheEMJ-` of :the battery 40. As the range yof the target isdecreased, the motor speed isA increased and its back acts Vto reduce.the current in the coils 33 and 34E-thereby reducing the radius ofthespot 56. The radius of the spot is then ameasure of the range of theVtarget and a suitably calibrated scale may be provided to indicate therange.

In the arrangement described it will be noted, that theV frequencydelivered by the variable oscillator 4 to the modulator 18 will notcorrespond to that of the received signal unless the frequency fdelivered from the radio amplifier 17 and the frequency componenti ofthe variable oscillator are the same. Therefore, no signal will passthrough the high frequency amplifier 19 tuned to fo unless theinstantaneous frequencies of the variable oscillator and the signal inthe radio frequency amplifier 17 differ by fo.

In addition to controlling the brightness of the cathode ray beamthrough the received impulseV provision 1sl also made for retarding orincreasing, the angular velocity` of the rotating system to bring theprojector into directive alignment with the incoming signal so thatthesignal will be received on both halves of the receivingV projector atthe same time instant. Under ordinary com..

ditions if the receiving projector is rotating too slowly for the rangebeing observed, the signal will arrive at the receiving station as theforemost projector is approaching the direction from which the beam isbeing reflected. In such a case a pulse is transmitted which will tendto increase the velocity lof rotation so that on the next revolution theecho will be received at the same time instant by` both the forward andthe rear projectors. Forward and rear in this case refer to thedirection of rotation of the projectors which are directed substantiallyin the same direction andwhich by means of the lag lead line 16 havetheir axes of reception separated by a small angle.

The circuit arrangement for providing this means is also shown inFig. 1. In this case the pulses from the different projectors ordifferent projector halves, after passing over the lag-lead line 16, aretransmitted to modulators 2'7 andg28, respectively,l intowhich isimpressed the frequencyfrornthe,variable frequency oscillator 4 as wellas a ,local ylow oscillator frequency 29 which may be of the order of300 cycles. This low frequency oscillation is impressed upon themodulators 27 and 28 in opposite phase. The outputs lof the modulators27 and 28 pass through an intermediate vfrequency amplifier 3ft whichwill amplify the fixed frequency fo when the echo set for the desiredrange is received. The output of the intermediate amplifier 3ft ispassed through a band filter 31 for Vfiltering the frequencycorresponding to that deliveredby the low frequency oscillator 29 withthe result that the output of the filter3?L produces a pulse with apositive or negative phase dependent upon whether the output of themodulator 27 or 28 is predominant in intensity. The output from thefilter 31 is impressed upon a phase-sensitive detector 32,V the outputof which, in turn, is superimposed upon a current flowing in thedeflection coils 33 andk 34 associated with the cathode ray tube 25. Ifthe range is short, the action of the current in the deflection coilsuperimposed by the phasesensitive detector 32 may be made such as tomake an inward serration of the spot towards the center of the circle bydecreasing momenarily the currentin the coils. A longer range may beindicated by an increase of current in the coils 33 and 34 which wouldmake an outward serration of the spot. This current in the deflectioncoils 33 and 34 is superimposed upon that produced by the controlcircuit which includes the driving motor 35, the speed of which may becontrolledby thevariable resistance adjustment 36 acting onthe grid 37of the gaseous conduction tube 38. By proper adjustment of the arm onthe resistance 36 the speed of the motor may be con trolled and set adesired value. The motor in this case will be a direct current motorwith alternating current impressed through the armature and the gaseousconduction tube which acts as a rectifier during the positive half ofthe alternating current cycle. A filter 39 is provided which produces asubstantially uniform ,direct current through the coils 33 and 34, thebattery 40being connected in series opposition to the voltage appearingacross the output of the filter 39.

The arrangement in Fig.l l just described willoperate to produce aninward or outward serration of the beam together with a brighteningk oftheA beam indicating the receipt of the signal. The beam may be, blankedout during transmission by connecting a rectifier 41 to the output ofthe power amplifier 13 and connecting the output of the rectifier to thecontrol grid 24 to produce a negative potential thereon duringtransmission of the signal.

In the arrangement indicated in Fig. 2 the circuit is shown from thephase-sensitive detector on to the ,cathode ray tube. In this casethecoils 33and 34 of the cathode ray tube are directly connected to thecathode 5t) of the thermionic tube 51, the anode-cathode circuitbeingreturned through'thegvmotor y35, the4 direct current supply sources52 and 53 connected in opposed relation',y

to each other with a ground 54- between the two direct current supplies.The back generated by the motor 35 will produce a potentialsubstantially proportional to the angular velocity of the motor 35 whichwill produce a corresponding current through the coils 33 and 34. Thiscurrent will be augmented or decreased by the pulse discharged from thephase-sensitive detector controlling the grid 55 of the thermionic tube51. This circuit arrangement in Fig. 2 may be employed in Fig. l forproducing the desired serration of the indicator spot 56 in the rotationof the cathode ray beam.

In the arrangement of Fig. 3 the pulse control from the phase-sensitivedetector on the grid 55 of the thermionic tube 51 is impressed throughthe condenser 57 and the impedance 58 upon a fullwave rectifier tube 59tied to ground through resistances 60 and 61 which control respectivelythe grids 62 and 63 of a pair of thermionic tubes 64 and 65 respectivelyoperating in a so-called push-pull relation. The outputs of the tubes 64and 65 will produce direct current pulses either in the eld windings 66or the eld windings 67 of the motor 68. These iield windings are set upfor reverse rotation so that if one is energized, the motor will operatein one direction while if the other is energized, the motor will operatein the reverse direction. 'Ihe motor 68 controls a potentiometer arm 69which may be driven through a reduction gear and which will be rotated asmall amount by the direct current pulse in the coil 66 or 67 either ina clockwise or counter clockwise rotation. The potentiometer arm 69controls the potential on the grid 37 of the tube 38 and this controlmay be made in series with the manually adjustable control 36corresponding to that of Fig. l. The pulse operation of the motor 68will operate with each received signal if there is a differential ofphase between that received on one receiving unit and that received onthe other receiving unit. In such a case the arm 69 will be moved asmall amount and remain in this position until successive signals mayadvance it one way or another. If a signal is missed or not received,then the motor 35 will still operate at the same speed as previouslyestablished until the arm 69 is manually reset. The motor 35 in Fig. 3corresponds to that in Figs. l and 2, the only diierence being that inFig. 3 there is superimposed the additional control effected through thepositioning of the potentiometer arm 69. An increased positive potentialon the grid 37 will speed up the motor 35 while a decrease of positivepotential will tend to decrease the motor speed. The motor 35, the speedof which is controlled both manually and automatically, establishes theangular velocity for the rotating system. The coils 33 and 34, thekeying commutator 1l and the projector and receivers 1 and 2. are allrotated at the same speed either through Selsyn control or through shafttransmission. The potentiometer arm S may be controlled from any one ofthe driving units or from its own driving unit provided it is driven attwice the speed of the other units.

In the operation of the system a signal will be received if the speed ofrotation of the receiver and projector is set for a range at which anobject is positioned. For instance, if in search at sea a target isobserved which is at a distance of 800 yards, it is well known that thetime interval between transmission and reception will be about onesecond so that the receiver must pass the position for the direction ofthe target one second after the signal was transmitted. lf this is thenthe observing range of the system, it will follow that two projectorssending and receiving placed back to back must make one revolution intwo seconds in order for the receiver to be in position to receive theecho reflected from the distance of 800 yards. l

By the arrangement or" Fig. 3 if the echo is received from a positionslightly less or greater than the set distance, then an automaticadjustment will be made to bring theecho in corrected range insuccessive observa- 6 tions unless, of course, the target is moving sorapidly that it may get out of range between successive signalingperiods. The arrangement of Fig. 3 will further permit the target to befollowed in or out of its course and therefore provide a continuousindica-tion for the observer. The deection of the cathode ray beam andits rotation may be controlled by electrostatic plates instead of thedeflecting coils as shown. Instead of rotating the coils or plates torotate the beam, the electrostatic or electromagnetic lield may berotated in a manner known in the art.

Having now described my invention, I claim:

1. A system for ranging comprising, in combination, means for producinga directive beam of compressional wave energy only during the timeinterval the beam is rotated through a desired sector of arc, means forrotating the compressional wave beam through said desired sector of arcat a given angular velocity, means simultaneously varying the frequencyof the beam during its sweep of said arc continuously in increasing ordecreasing value, means for directively receiving the compressional wavebeam, means for rotating said receiving means through the desired sectorat the said angular velocity after the compressional beam has beenrotated through the said sector and selectively tuning the same forreception of reilection arriving from a given distance and a cathode raytube indicating means having a cathode beam adapted to be rotated insynchronism with the receiving means at aV radius corresponding to thegiven distance and means operative from said receiving means on saidcathode beam to produce an indication thereof on the screen of thecathode ray tube.

2. A system for sounding ranging comprising, in combination, means forproducing a directive beam of compressional wave energy only during thetime interval the beam is rotated through a desired sector of arc, meansfor rotating said beam through said desired sector yof arc at a givenangular velocity, means for directively receiving the compressional wavebeam, means for rotating said receiving means through the desired sectorafter the compressional beam hasA been rotated through Vthe said sectorat the same angular velocity as for the rotation of the said beam and acathode ray tube indicating means having a cathode ray beam, means forrotating the cathode ray beam in synchronism with the receiving means,means maintaining said rotation of the cathode ray beam at a radiuscorresponding to a given distance being observed and means operative onsaid cathode beam to produce an indication of a reection being receivedfrom the given distance.

3. A system for ranging comprising, in combination, means for producinga directive beam of compressional wave energy only during the timeinterval the beam is rotated through a desired sector of arc, means forrotating the compressional wave beam through said desired sector of areat a given angular velocity, means simultaneously varying Ithe frequencyof the beam during its sweep of said arc continuously in increasing ordecreasing values, means for directively receiving the compressionalwave beam, means for rotating said receiving means through the desiredsector at the said angular velocity after the compressional beam hasbeen rotated through the said sector and for continually tuning thereceiving means during its rotation of the arc from which a reflectionis to return corresponding to the frequency which was emitted at thesame point, a cathode ray tube indicating means having a cathode beam,means for rotating said cathode beam at a radius corresponding to agiven distance being observed and means operative from said receivingmeans on said cathode ray beam to produce an indication on the screen ofthe cathode ray tube.

4. A system for ranging comprising, in combination, means for producinga directive beam of compressional wave energy only during the timeinterval the beam is 7". rotated through a desired sector of arc, meansfor rotating the .compressional wave beam -through said desired sectorof arc-at a given angular velocity, means simultaneously varying the-frequency of the. beam during its sweep of said arc continuously inincreasing or decreasing values, vmeans. for directively receiving thecompressional `wave beam, meansfor Arotating said receiving meansthrough the desired sector at the Vsaid angular velocity after thekcompressional beam-has been rotated through the said sector andforcontinually tuning the receiving means duringA its rotation of the arcfrom which a reflection is to return corresponding to the frequencywhich was emitted kat the same point, a cathode ray tube indicatingmeans having -a cathodebeam, means forl rotating said cathode-l beam ata radius corresponding to a given distance being observed and meansoperative from said receiving -means on said cathode ray beamto producean indication on .the screen of the cathode ray tube, said last-named.means includingl a control grid normally suppressing the beam on which apositive potential is impressed from said receiving means for making;vthe beam momentarily visible.

5. in a system for sound ranging including means for rotating a beam ofcompressional waves in a desired sector being observed, a receivingprojector system including two units positioned with respect to oneanother to receive from slightly diiferent directions, means forro-tating said projector at the same velocity at which the beam wasrotated over the arc of said beam, and means operativeby the signalreceived on said projector for indicating on which unit said receptionwas obtained including a cathode ray tube indicating means having acathode beam with -means for rotating the beam at a radius correspondingto a given range being observed and at the same angular velocity atwhich the receiving proiector is rotated with means for producing aditerent radial serration of said beam depending upon whether theindication was received on one or the other units of said receivingprojector.

6. In a system for sound ranging including means for rotating a beam ofcompressional waves in a desired sector being observed, a receivingprojector system including two units positioned with respect to oneanother to receive from slightly dilerent directions, means for rotatingsaid projector at the same velocity at which the beam was rotated overthe arc of said beam, and means operative by the signal received on saidproiector for indicating on which unit said reception was obtainedincluding a cathode ray tube indicating means having a cathode beam withmeans for rotating the beam at a radius corresponding to a given rangebeing observed and at the same angular velocity at which the receivingprojector is rotated with means for producing a ditferent radialserration of said beam depending upon whether the indication wasreceived on one or the other units of said receiving projector, andmeans operative through said signal received by said receiving means forchanging the speed of rotation of the system including that of therotation of the compressional wave beam, of the receiving projector andof the cathode beam in accordance with the indication by said receiverof said serration indicating whether the range is too small or toogreat.

7. In a system for obstacle detection using a directive beam of waveenergy, means for directly receiving the wave energy reflected from theobject whose location and distance are to be determined, means forsweeping the receiving means periodically over an arc covering the areabeing observed and means controlled by the relation between the positionof the receiving means and the arrival of the echo from the obstacle atthe receiving means for effecting an increase or decrease in the rate ofsweep of the receiving means to provide a synchronization of thecoincidence of the arrival of the echo and the positionof the receivingmeans..

8. .In a system` fomobstaclerdetection, meansfor propa-v 8 gating adirective beam of wave energy, means for sweeping the beam over the arcof the area being observed, means for. directively receiving wave energyreliected from the object whose direction and distance are to beYdeterrnined,said means including units having directive right and leftsense, means fory sweeping the receiving means periodically over thesame area being observed and means operatively controlled by therelation of the instantaneous position of the receiving means and thevarrival of the reflected signal from the obstacle being observed at thereceiving means for effecting an increase or decrease in the rate ofsweep of the receiving means to providesynchronization of thecoincidence of the arrival 0f the reflected signal and the position ofthe receiving "means during successive periodic .sweeps of bothpropagating and receiving means.

9. In a system for obstacle detection employing a directive propagatingbeam of wave energy swept periodically Vover-an area being observed,means for directively receiving the wave energy retlected from theobject whose direction and distance are to be determined, means forsweeping the receiving means periodically over the area being observedand means controlled by the relation between` the position of thereceiving means and the arrival of the echo from the obstacle at thereceiving means for effecting an increase or decrease in the rate ofsweep of the receiving means to provide a synchronization of thecoincidence of the arrival of the echo and the position of the receivingmeans, said control means including a motorL for rotating the receivingmeans and means controlling the speed of the motor including thermionictubes and circuits operatively associated with the receiver forproviding an increase or decrease in the motor speed dependent .uponsaid relation between the position of the receiving means and thearrival of the echo.

10. Lina system for obstacle detection using a directive beamof waveenergy swept periodically over the area observed and a directivereceiving means having a right and left sense for providing anindication whether the reflection is received to the right or left ofthe receiving means, a motor for rotating the receiving means andsweeping the samer over the area being observed, means for controllingthe angular velocity of sweep by said motor including variablemeans forregulating the voltage control of said motor, and means for developingan electric .pulse in accordance with the right or left indication ofthe receiving meansfor operating said voltage-varying means .to controlthe speed of said motor.

11. In a system for obstacle detection using a directive beam` of.,waveenergy. swept periodically over the area observed and a directivereceiving means including two units having directive axes oriented indirections forming an acute angle, a motor for rotating the receivingmeans and sweeping the same over the area being observed,

Vmeans for controlling the angular velocity of sweep by said motorincludingtmeans for varying the speed of the motor, saidY last-namedmeans including a source providing an electric pulse acting upon thespeed control means to increase or decrease the motor speed in'accordance with the unit upon which the greater amount of wave energywas received,

l2. In a `system for obstacle detection using a directive beam of waveenergy swept periodically over the area observed and a directivereceiving means including two units having directive axes oriented indirections forming an acute angle, a motor having a iield winding forrotating the receiving means and sweeping the same over the area beingobserved, means for controlling the angular velocity of sweep by saidmotor including potentiometer means and a second motor means for varyinga tap of said potentiometer for controlling the current inthe fieldwinding of said first-named motor and means for impressing an electricpulse upon said second motorio efiecta changent operating positionthereof 9 according to whether a greater amount of energy was receivedon one receiving unit than on the other.

13. In a system for obstacle detection using a directive beam of waveenergy swept periodically over the area observed and a directivereceiving means including two units having directive axes oriented indirections forming an acute angle, motor means having a eld winding frrotating both the transmitting and receiving means at substantially thesame velocity for picking up a reecton from an obstacle at a givendistance range, means for controlling the angular velocity of sweep bythe motor including potentiometer means for controlling the currentsupplied to the eld winding of said motor and a second motor means foroperating said potentiometer, said second motor means being operated inpulses l5 by the received signal to advance or retract the potentiometerarm setting for varying the rst-named motor 10 speed with each pulse inaccordance with the predomi nance of one signal over the other receivedby said receiving means.

References Cited in the tile of this patent UNITED STATES PATENTS1,973,673 Rice sept. 11, 1934 2,011,392 Bentley Aug. 13, 1935 2,130,913Tolson Sept. 20, 1938 2,231,929 Lyman Feb. 18, 1941 2,236,893 ChaieeApr. 1, 1941 2,399,017 Goldman Apr. 23, 1946 FOREIGN PATENTS 497,147Great Britain Dec. 9, 1938 546,202 Great Britain July 2, 1942 UNITEDSTATES PATENT oEEICE CERTFICATION UF CUEUHUN Patent No, 2962,694November` 29v 1960 Laurence Batcheloler It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 4, line llY for "momenarily" read momentarily line 5l, after"set" insert -e at -w column 7Y line 64, for "directly" read directivelyuw.

Signed and sealed this 30th day of May l9l (SEAL) Attest:

ERNEST W. SWIDER y DAVID L. LADD Attesting Gizficeri Commissioner ofPatents ERNEST W. SWIDER Attesting Officert UNITED STATES PATENT oEEICECERTIFICATION OF CORRECTION Patent No, 2,962,694 November 29XI 1960Laurence Batchelder Column 4, line 4lY for "momenarily" read-fmomentarily line 5l, after "set" :'LlnserrI e at we column 7, line 64,for "directly read directvely ma Signed and sealed this 30th day of May1961.,

(SEAL) Attest:

DAVID L. LADD Commissioner of Patents

